Uterine Protein secretions may serve as a histotrophic nutrient source and provide some regulltory functions in blastocyst development. Our aim is to purify and characterize proteins secreted by the procine uterus under the influence of progesterone and evaluate their functions as enzymes and as binding or transport molecules for steroids vitamins and minerals. The effect of sex steroids on structural and compositional changes in the endometrial surface epithelium will be evaluated in an attempt to better understand the process of placentation. Sex steroid effects on endometrial metabolism of progesterone to androgens will be studies with the aim of understanding intiation and control of steroidogenesis (androgen conversion to estrogens) by the blastocyst. The effect of sex steroids on enzymes affecting carbohydrate metabolism will be studied to determine the significance of the phosphogluconate pathway in providing NADPH, ribose sugars and energy substrate to the blastocyst. These experiments will allow us to better understand progesterone-induced proteins in uterine secretions and epithelial cell membranes which may be intimately involved in regulating blastocyst development, initiation of steroidogenesis and placentation. This information may be useful in developing means for either enhancing or inhibiting fertility.